1. Technical Field
The present invention relates to a diamond wire drawing die and a process for manufacturing a diamond wire drawing die.
2. Background Art
A drawing die is a tool used for drawing wire, such as a metal wire. Such dies must have enough strength to avoid breakage during drawing, must have superior wear resistance, must be capable of being shaped into an appropriate structure and form, and must have a final die hole surface which provides appropriate drawing conditions.
Diamond, which has all of these properties, is a superior raw material for a wire drawing die. Diamond is the hardest known material and has the highest modulus of elasticity of all known materials. Furthermore, extremely pure diamond has the highest thermal conductivity and the highest transmittance in the infrared spectrum. Thus, diamond is a material for which there are no comparable substitutes with respect to wire drawing dies.
Natural single crystal diamonds, synthesized single crystal diamonds and polycrystalline diamond composites have all been used as a central portion of a wire drawing die. EP 0,391,418 A1 relates to a diamond wire drawing die made of synthesized single crystal diamond provided by the temperature gradient method, and describes a method of producing wire drawing dies by cleaving diamond. However, natural single crystal diamonds and synthesized single crystal diamonds are expensive and are limited in crystal size. Such diamonds are easy to cleave and are prone to breakage.
Polycrystalline diamond composites overcome the faults of single crystal diamonds. A method of synthesizing diamond from a gaseous phase is disclosed in U.S. Pat. No. 4,767,608 issued Aug. 30, 1988 to Matsumoto, et al. Furthermore, U.S. Pat. No. 4,434,188 issued Feb. 28, 1984 to Kano et al. discloses synthesizing diamond from a gaseous phase. With respect to the wire drawing die, a polycrystalline diamond composite is disclosed in U.S. Pat. No. 3,831,428 issued Aug. 27, 1974 Wentorf, Jr. wherein the composite wire drawing die construction is described in which a centrally located mass of diamond defines at least the throat of the wire drawing hole, the mass being flanked or girded by at least one mass of metal bonded carbide that is directly bonded thereto. However, polycrystalline diamonds are limited with respect to wear and heat resistance because they contain sintering aids.